Elsevier

Surface Science

Volume 572, Issue 1, 10 November 2004, Pages 115-125
Surface Science

Diffusion-limited electrodeposition of ultrathin Au films on Pt(1 1 1)

https://doi.org/10.1016/j.susc.2004.07.055Get rights and content

Abstract

The electrodeposition of Au on Pt(1 1 1) from electrolytes containing μM concentrations of AuCl4- was studied by in situ scanning tunneling microscopy. Under these conditions the Au flux is limited by diffusion in the electrolyte over a wide potential range, which allows to assess the effect of the electrochemical environment on the growth kinetics. Similar to gas phase metal deposition Au film growth proceeds via nucleation and lateral growth of Au monolayer islands, with the saturation island density strongly depending on the deposition potential and on the anion species in the electrolyte. For deposition in H2SO4 solution the saturation island density continuously increases with increasing potential between −0.2 and 0.5 V (SCE), whereas in Cl-containing H2SO4 it first decreases and then increases again. Following nucleation and growth theories this behavior can be attributed to potential-induced changes of the Au surface mobility, caused by changes in the density and structure of coadsorbed sulfate/bisulfate and chloride adlayers. Under conditions of high Au surface mobility multilayer growth proceeds via a typical Stranski–Krastanov growth mode, with layer-by-layer growth of a pseudomorphic Au film up to 2 ML and 3D growth of structurally relaxed islands at higher coverage, indicating thermodynamic control under these conditions.

Introduction

The electrodeposition of metals is one of the most important processes in electrochemistry [1]. Basic aspects of the growth process have been investigated in model studies on the electrodeposition of ultrathin metal films and nanostructures, with coverages ranging from submonolayer amounts to a few atomic layers. In recent years modern structure sensitive in situ techniques such as scanning tunneling microscopy (STM) or atomic force microscopy (AFM) have greatly contributed to the understanding of these growth processes on the atomic scale. For instance, the initial stages of the deposition of thin magnetic films were investigated this way [2], [3], [4], [5]. Unlike gas phase metal deposition, e.g., via molecular beam epitaxy (MBE), fundamental studies of the electrodeposition of ultrathin metal films are often performed under conditions close to equilibrium, where the thickness and morphology of the resulting film are controlled by the thermodynamic properties of the respective system. A typical example are studies on the underpotential deposition (UPD) of mono- or bilayer metal films [1]. In contrast, the influence of the growth kinetics on the atomistic growth process and on the resulting atomic-scale film morphology, which has been intensively studied experimentally and theoretically for MBE growth (see [6], [7] and references therein), has attracted much less interest so far. Finally also the deposition potential has to be considered as an important additional parameter compared to gas phase deposition, which not only determines the kinetics of the ion transfer reaction, but also may affect the deposition process by changing the condition of the electrode surface. Examples for the latter are direct modifications of the properties of the deposited metal adatoms or indirect effects, e.g., caused by anion coadsorption. The lower interest in atomistic kinetic studies results from an experimental problem: In most experiments the deposition rate is varied together with the deposition potential, and therefore kinetic effects can hardly be separated from potential effects.

In the present paper we present and discuss in situ STM data on the growth behavior of ultrathin metal films electrodeposited under conditions where kinetic growth theories commonly used in UHV can apply. This was achieved by an alternative method, electrodeposition at high overpotentials limited by diffusion in the electrolyte, using Au electrodeposition on Pt(1 1 1) as an example. This procedure allows to independently control the potential and the deposition rate over a wide range of potentials and rates, which makes it possible to separate the influence of these two effects on the atomic-scale morphology of the deposit.

In diffusion-limited deposition at high overpotentials the metal ions or complexes in solution that arrive at the electrode surface are immediately discharged and redissolution back into the electrolyte is negligible. Hence, the deposition process occurs under conditions far from equilibrium, which resembles the situation found for MBE growth under ultrahigh vacuum (UHV) conditions, and one would expect kinetic growth theories to give a proper description of the growth process [8], [9]. According to these theories, the temporal evolution of the deposit morphology, including, e.g., the density of adlayer islands during the initial nucleation phase, the island shape during the subsequent lateral growth of monolayer islands or the film roughness during vertical growth, depend on the deposition rate and deposition temperature as experimental parameters and on system properties such as the binding energy of small admetal clusters and the mobility of metal adatoms on the flat terraces as well as along or across substrate or deposit steps [8], [9], [10], [11], [12], [13], [14], [15]. The metal flux in diffusion-limited electrodeposition is determined by the concentration of the metal species in solution, its (temperature-dependent) diffusion coefficient in the electrolyte, and the hydrodynamic conditions. It approaches a fixed value after an initial period where a steady-state diffusion profile evolves in front of the surface. The surface mobility of the deposited metal adatoms depends on the interface structure, which includes the presence of coadsorbed species (solvent molecules, anions), and on the surface charge. Consequently it strongly depends on the electrolyte composition and potential, as will be shown in this work.

The present report follows in situ STM studies of ultrathin Au films on Pt(1 1 1) [16] and AuPd films on Au(1 1 1) [17] formed by diffusion-limited electrodeposition from highly diluted solutions of the metal salts. Here we discuss for Au/Pt(1 1 1) in detail the nucleation and growth of these films from submonolayer up to multilayer coverages. After a brief description of the experimental setup and procedures we will first concentrate on the effect of the deposition potential on the nucleation and two dimensional (2D) growth behavior of monolayer Au islands on Pt(1 1 1) in Cl-free sulfuric acid solution, then evaluate the influence of strongly adsorbing anions by comparing with data obtained in Cl-containing electrolyte, and finally investigate the multilayer growth behavior up to coverages of a few Au monolayers. The data demonstrate a large potential effect on the 2D nucleation and growth behavior, which is interpreted in terms of a modified surface mobility of the Au adatoms.

Section snippets

Experimental

A Pt(1 1 1) single crystal (Mateck), cut and oriented to better than 0.1°, was used as substrate. Before each deposition experiment, the surface was freshly prepared by electrochemical oxidation in 1 M HClO4 (1 min) and chemical dissolution of the oxide in 10% HCl (10 s). Subsequently, the crystal was annealed in a H2/air flame for 5 min, cooled down in a H2/N2 (2:98) stream, protected by a drop of Milli-Q water, and then transferred into an electrochemical cell. All solutions were made from Milli-Q

Electrochemical measurements

Prior to the STM measurements the electrochemical behavior of the samples was characterized by cyclic voltammetry in a separate electrochemical cell using a hanging meniscus configuration (Fig. 1). For a Au-free sample which has been transferred directly after flame annealing (Fig. 1a) the voltammogram exhibits the typical features of a clean Pt(1 1 1) electrode surface [21], whereas after deposition of 1.5 ML of Au a completely different voltammogram is found (Fig. 1b). In particular, the

Conclusions

We have demonstrated for Au electrodeposition on Pt(1 1 1), that electrodeposition under diffusion-limited conditions, from highly diluted solutions, and at high overpotentials allows to investigate metal deposition under well-defined, kinetically controlled conditions and to clearly separate effects from growth kinetics and potential effects. The resulting deposit morphologies closely resemble those obtained for gas phase deposition and can be explained by kinetic growth theories. The method can

Acknowledgments

We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft and by the Centre National de la Recherche Scientifique as well as fellowships for F.M. and E.S. by the Alexander von Humboldt-foundation and for F.M. by the ‘Délégation Générale pour l’Armement’ of France.

References (40)

  • M.C. Bartelt et al.

    Surf. Sci.

    (1999)
  • Z. Shi et al.

    J. Electroanal. Chem.

    (1994)
  • Z. Shi et al.

    J. Electroanal. Chem.

    (1996)
  • J. Wiechers et al.

    J. Electroanal. Chem.

    (1988)
  • J. Clavilier et al.

    J. Electroanal. Chem.

    (1980)
  • W. Savich et al.

    J. Electroanal. Chem.

    (1995)
  • N. Li et al.

    J. Electroanal. Chem.

    (2000)
  • A.M. Funtikov et al.

    Surf. Sci.

    (1995)
  • A.M. Funtikov et al.

    J. Electroanal. Chem.

    (1997)
  • R.J. Nichols et al.

    J. Electroanal. Chem.

    (1990)
  • E. Budevski et al.

    Electrochemical Phase Formation and Growth

    (1996)
  • F. Möller et al.

    Phys. Rev. B

    (1997)
  • S. Morin et al.

    Phys. Rev. Lett.

    (1999)
  • W. Schindler et al.

    Phys. Rev. B

    (1997)
  • A. Gundel et al.

    Phys. Chem. Chem. Phys.

    (2001)
  • H. Brune et al.
  • P.A. Thiel et al.

    J. Phys. Chem. B

    (2000)
  • J.A. Venables et al.

    Rep. Prog. Phys.

    (1984)
  • H. Brune

    Surf. Sci. Rep.

    (1998)
  • T.A. Witten et al.

    Phys. Rev. Lett.

    (1981)
  • Cited by (30)

    • Dendritic growth of the Pt–Cu islands on Cu(111) surface: Self-learning kinetic Monte Carlo simulations

      2019, Surface Science
      Citation Excerpt :

      In such situations dendritic islands with threefold symmetry are observed. Electrodeposition of Au atoms on Pt(111) substrate with negative deposition potential results in formation of dendritic islands with the threefold symmetry [8]. Scanning tunneling microscope (STM) experiments [2] show that Co atoms arrange into dendritic islands on Cu(111) surface at temperatures lower than 300 K.

    • Improvement in the activity of Pt<inf>1</inf>Ni<inf>3</inf>/C by decorating with Au adatoms for ethylene glycol oxidation

      2018, International Journal of Hydrogen Energy
      Citation Excerpt :

      The other one is the change in the property of Pt1Ni3 nanoparticles by Au adatoms through ligand effect and strain effect. The ligand effect can be caused by the interatomic charge transfer between Au and Pt [18,41] and between Au and Ni2+ [42], and the strain effect results from a lattice mismatch of 4.2% for Au and Pt [43] and of 15.7% for Au and Ni [44]. The interaction between Au adatoms and Pt surface atoms is believed to play an important role, but the interaction between Au adatoms and Ni surface atoms/ions may also play a role.

    • Anion effects on the interfacial alloying in successively electrodeposited Cu and Au ultrathin films

      2018, Journal of Alloys and Compounds
      Citation Excerpt :

      In certain cases, adsorbed anions increase the coordination number of metal ad-atoms that, in turn, results in the improvement of their surface mobility, which in electrodeposition promotes large crystallite formation [29,31,32]. For example, simply changing the supporting electrolyte from sulfate to chloride has been shown to have a specific impact on the deposition growth mode of Au on Pt [33]. It has also been shown by Ye et al. that specifically adsorbed chloride can stabilize specific step-edges of a Au (111) surface inhibiting dissolution [34].

    • Improved activity and different performances of reduced graphene oxide-supported Pt nanoparticles modified with a small amount of Au in the electrooxidation of ethylene glycol and glycerol

      2016, Electrochimica Acta
      Citation Excerpt :

      At the same time, the contribution of other factors is also probable. For example, the potential of +0.50 V selected in this study for the deposition of Au on Pt/RGO is a relatively high value, thus the formation of Au clusters of small size and the increase in the density of Au clusters on the surfaces of Pt nanoparticles, as reported for the electrodepositon of Au on Pt(111) [27], are considered, which is favorable for the synergistic effect between Pt and Au. A faster rate of removal of the surface adsorbates (-CHxO) on the Au-Pt catalysts has also been reported [47].

    View all citing articles on Scopus
    1

    Present address: Laboratoire de Catalyse en Chimie Organique, CNRS UMR 6503, Université de Poitiers, 40, avenue du Recteur Pineau, F-86022 Poitiers, France.

    2

    Address: Laboratoire de Physique de la Matière Condensée, CNRS-École Polytechnique, F-91128 Palaiseau, France.

    3

    Present address: Laboratoire de Physique de la Matière Condensée, CNRS-École Polytechnique, F-91128 Palaiseau, France.

    View full text